The present disclosure relates to shape memory alloys and it use, and more particularly to the use of a shape memory alloy in an air-cooled oil cooler system of an aviation engine.
Aviation engines use oil to dissipate heat from engine components, such as engine bearings, electrical generators, and the like. Heat is typically rejected from the oil to air by air cooled oil coolers (ACOC), and more particularly, surface air-cooled oil cooler (ACOC) systems to maintain oil temperatures at a desired ˜100° F.<T<300° F. In many instances an environment may be as low as −65° F. When this occurs, a bypass valve may be incorporated to allow a portion of the oil to bypass the air cooled oil cooler and return to the engine without being cooled by the air cooled oil cooler, if required.
Known bypass valves for use in air-cooled oil cooler systems of aviation engines typically include pressure actuated valves that are responsive to an increase in pressure, and pressure and thermally actuated valves that are responsive to an increase in both pressure and temperature. Pressure actuated valves are well known in the art, but are not easily tunable. Pressure and thermally actuated valves are also known in the art and typically comprise a valve driven by dual springs and a thermal actuator based on the volume change of a wax contained therein that is subject to a change in phase from a solid to a liquid in response to an increase in temperature. Pressure and thermally actuated bypass valves, while providing a sufficient means for allowing a portion of the oil to return to the engine without being cooled, are unreliable due to sealing issues and the like. In this type of valve, the wax in liquid phase has a tendency to leak and therefore the reliability of the valve is typically lower than desired. In addition, the inclusion of dual springs results in a component of a weight and a cost that may be of issue.
It would therefore be desirable to provide a robust pressure and thermally actuated bypass valve for use in an air-cooled oil cooler system for an aviation engine that addresses the above issues.